1. Field of the Invention
The invention relates to a compound having a hard polyoxymethylene component and a soft thermoplastic styrene elastomer component, and to a process for producing a composite body from such compound.
2. Description of the Related Art
Compounds having hard and soft components or composite bodies and the process for producing such compounds or composite bodies are described, for example, in WO 00/20204 and DE 198 45 235. These references require the use of a relatively expensive non-olefinic thermoplastic material, which requires expenditure during compounding, in the form of polyester-urethane elastomers, polyether-urethane elastomers, polyesters, polyamides, polycarbonates or polyacrylates. An improvement in the adhesion between polyoxymethylene (POM) and elastomers of the thermoplastic styrene elastomer (TPE-S) type is said to be achieved by this means. This pairing of materials has also been presented at various technical conferences, such as “Thermoplastic Elastomers” at SKZ Würzburg, May 1999 and Jun. 2000, at which, however, the mechanical properties, the resistance and the bonding adhesion values according to the general state of knowledge were rated as too low for many cases of use. The multicomponent injection molding process has been disclosed for the production of a composite body, and enjoys a constantly increasing demand because the properties of hard and soft materials in one composite body can be combined in one production step.
The combination of POM with TPE-S is of particular interest, because both materials are distinguished by a number of unique properties.
POM is known for: outstanding mechanical properties (high tensile strength, impact strength, rigidity, fatigue resistance); excellent resistance to moisture, motor fuel, lubricants, solvents, neutral chemicals; excellent dimensional accuracy; good electrical insulation properties; creep resistance; low friction; and a broad operating temperature range.
POM is employed in the automotive, domestic appliance, installation, machinery, tool, electronics and consumer goods industries. POM is used for many moving parts, such as gear components, deflection pulleys, toothed wheels or adjusting levers, due to its good sliding friction properties, and is used for snap connections, due to its excellent rebound resilience.
Thermoplastic elastomer (TPE) is known for: widely variable hardness range (Shore A=10 to Shore D=60); low density; good recovery properties; outstanding mechanical properties; high noise-damping; good aging properties and outstanding ozone properties; wide flexibility range and comparatively small change in flexibility in a wide operating temperature range; good resistance to acids and alkalis; and very good static friction.
Thermoplastic styrene elastomer (TPE-S) is used in the same and similar branches of industry as polyoxymethylene (e.g., automotive industry, domestic appliance industry).
In particular, there is therefore a need for a combination of a POM component and one or more TPE-S components, such as hydrogenated styrene block copolymer, in which the adhesion between the two components is greatly improved compared with the prior art so as to make possible the wider use of a combination of POM/TPE-S in multicomponent injection molding, without the need for mechanical anchorings, such as expensive undercuts, being necessary.